This application claims priority to International Application No. PCT/US00/13617, filed May 17, 2000, which was published under PCT Article 21(2) in English, and claims priority to Japanese Application No. 11-140204, filed, May 20, 1999, from which PCT/US00/13617 claims priority.
The present invention relates to adhesive/sealant compositions, and more particularly to an adhesive/sealant composition used for sealing a joint, a step, a bond portion, a seam portion, a crack portion or other portions (hereinafter these portions being referred to as xe2x80x9cdiscontinuous portionsxe2x80x9d) of vehicles, for example, and a bonded structure in which the adhesive/sealant composition is used.
Vehicles such as automobiles and trucks have discontinuous joints formed by overlapping metal panels. The discontinuous joints are usually sealed with a sealant. One example of a common non-planar overlapping type joint is represented by a roof ditch formed in the front and back direction of a vehicle by bending the edges of the roof panel and side panels thereof and overlapping the bent portions. The roof ditch has a U-shaped channel, which also plays the role of collecting and discharging water, etc.
The sealant is supplied as a liquid or paste material in response to the requirement of execution of works. For example, in the automobile industry, a joint is usually sealed with a liquid plastisol. However, when the sealant is in a liquid state, there are areas in the roof ditch where the slope of the ditch makes it difficult to apply a liquid. Additionally, pastes need to be spread in the ditch by the operator and requires a certain level of skill to produce a seal that is aesthetically pleasing as well as functional. Accordingly, a sealant showing tackiness, having a definite shape and being molded in, for example, a sheet-like form must be used in some cases.
A heat-fusible and flowable adhesive tape has been used as a molded sealant. Adhesive compositions for such a tape are disclosed in, for example, U.S. Pat. No. 5,086,088, National Unexamined Patent Publication (Kohyo) No. 9-505334 and European Patent No. 798,354. The adhesive compositions contain an epoxy-containing material capable of being thermoset and an acrylic component having a nitrogen atom within the molecule.
However, when the acrylic component contains a nitrogen atom as explained above, the nitrogen atom generally enhances the polarity, and as a result the sealant, namely, the adhesive composition is hydrophilic. Thus, the adhesive composition tends to absorb moisture. Such moisture absorption is particularly significant, for example, in the coating line of automobiles in summer when the line is subjected to high temperature and humidity. Moisture absorption may also take place in winter as well due to dew condensation.
When a sealant that has absorbed moisture is applied to a roof ditch, the sealant foams and expands upon heating due to the absorbed water. As a result, the adhesive/sealant composition may not bond sufficiently to a discontinuous portion to cause lamination, or it may be lifted. Such delamination or lifting not only allows intrusion of dust, moisture and other undesirable components, but also causes a poor coating appearance and deteriorated bonding with an applied coating (e.g., automobile grade primer for paint).
On the other hand, National Unexamined Patent Publication (Kohyo) No. 9-505095 discloses a sealant containing a photo-copolymer having low affinity with moisture and an epoxy-containing material capable of being thermoset. For such a sealant, the photo-copolymer is selected so that the epoxy-containing material has compatibility with the photo-copolymer and so that the sealant can be applied to such an adherend having a low surface energy as a steel sheet having an oily surface. Therefore, a coating (e.g., a primer, paint, etc.) applied to the sealant adheres to the sealant only with insufficient strength. In extreme cases, such a sealant may repel the coating.
WO 98/21287 relates to thermosettable adhesive and photopolymerizable precursor of a pressure-sensitive thermosettable adhesive, which are useful for bonding plastic substrates to other substrates.
WO 96/32453 relates to a method for imparting topographical or protective features to a substrate by contacting a sheet material comprising a thermosettable layer with a substrate and heating the sheet material.
The adhesive/sealant composition of the present invention can have a desired appearance upon being coated (e.g., painted) and can have solvent resistance while effectively sealing a discontinuous portion with reduced moisture absorption.
In addition, the adhesive/sealant composition of the present invention can resist absorbing water upon exposure to high humidity before thermoset curing and thus can provide a smooth surface appearance and effective seal after curing.
In one aspect of the present invention, an adhesive/sealant composition having at least one of adhesive and sealing properties is provided. The adhesive/sealant composition comprises a radiation polymerizable vinyl material containing a vinyl type monomer which can exhibit a solubility parameter of 10 to 14 (cal/cm3)0.5, more preferably 10 to 12 (cal/cm3)0.5, when the monomer is polymerized to a homopolymer, a polymerization initiator for radiation polymerizing the vinyl material, a thermosetting epoxy-containing material and a heat-activatable hardener for the epoxy-containing material.
Preferably the radiation-polymerizable vinyl material contains a vinyl type monomer capable of exhibiting a solubility parameter of 10 to 14 (cal/cm3)0.5, and more preferably 10 to 12 (cal/cm3)0.5, when the vinyl type monomer is polymerized to a homopolymer.
In another aspect, the present invention relates to a bonded structure comprising an adherend having a discontinuous portion, and an adhesive/sealant composition which seals the discontinuous portion of the adherend, in which the adhesive/sealant composition is that of the present invention.
In still another aspect thereof, the present invention relates to a bonded structure comprising an adherend having a discontinuous portion, a plasticizer-containing plastisol which is applied to the discontinuous portion to seal the portion, and an adhesive/sealant composition which is at least partially provided onto the plastisol, in which the adhesive/sealant composition is that of the present invention.